Double Trouble: A Case of Central Hypothyroidism Following Primary Hyperthyroidism

Introduction: Maternal Graves disease is known to cause various forms of thyroid dysfunction in newborns. The manifestations include neonatal thyrotoxicosis, euthyroidism and transient hypothyroxinemia. Here we describe a case of central hypothyroidism following transient neonatal thyrotoxicosis. Case Presentation: A male child presented at 4 months of age with parents complaining of increased sweating and irritability. His birth weight was 3 kilograms and he was developmentally normal. His mother was treated for Graves disease that was TRAB positive (22 IU/mL) with methimazole earlier and changed to propylthiouracil during pregnancy. She was restarted on carbimazole 2 months postpartum, when she had presented to us. On physical examination, his length was 68.5 cm (+1 SD) and weight was 6.5 kg (-0.04 SD). He had tachycardia (136/min) and there was no thyromegaly. He was found to have hyperthyroidism on day 9 of life and was started on methimazole at 0.5 mg/kg per day. He was treated for 4 months elsewhere prior to referral. He was continued on methimazole at 0.15 mg per kg. The dose was titrated every 4 weeks and The TRAB level was 1.33 IU/L. At 8 months of age he was found to be euthyroid on a dose as low as 0.07 mg per kg per day. So, methimazole was withheld and he was followed up every 4-8 weeks. At 13 months of age, his laboratory reports were suggestive of central hypothyroidism and he was started on thyroxine supplementation. The dose of levothyroxine was adjusted every 8 weeks and he is under follow-up. Discussion: This case showcases the rare phenomenon of neonatal thyrotoxicosis followed by central hypothyroidism in the same infant born to a mother with Graves disease. The hyperthyroidism in this case could be due to transfer of maternal thyroid stimulating antibodies. The level of TRAB was within normal limits in the child and so the possibility of waning levels of TRAB could be considered as the value was not available at initial presentation. The central hypothyroidism could be due to exposure of high levels of maternal thyroid hormones in the last trimester leading to the suppression of hypothalamo-pituitary axis. Conclusion: This case highlights the significance of performing complete thyroid hormone profile in newborns born to mothers with Graves disease and the need for long-term close monitoring.